JPWO2013018607A1 - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

To provide a non-aqueous electrolyte secondary battery excellent in charge / discharge cycle characteristics at a high temperature even when the charge potential is increased. A non-aqueous electrolyte secondary battery according to the present invention includes LiNixCoyMn1-x-yO2 (0.9≰a≰1.1, 0 <x <1, 0 <y <1, 2x ≧) as a positive electrode active material. 1-y) containing at least 1% by mass of nickel cobalt lithium manganate, and in the positive electrode active material mixture layer, molybdenum oxide (MoOz; 2≰z≰3) is changed to nickel cobalt lithium manganate. It is characterized by containing 0.01 to 3.0% by mass. [Selection figure] None

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, in particular, having lithium nickel cobalt manganate as a positive electrode active material and containing molybdenum oxide in a positive electrode active material mixture, and excellent in high-temperature cycle characteristics even at a high charging voltage. The present invention relates to a non-aqueous electrolyte secondary battery.

  A non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery is widely used as a driving power source for portable electronic devices and a power source for hybrid electric vehicles (HEV) and electric vehicles (EV).

The positive electrode active material of these nonaqueous electrolyte secondary batteries is represented by LiMO ₂ (where M is at least one of Co, Ni, and Mn) capable of reversibly occluding and releasing lithium ions. lithium transition metal composite oxide to be, _{namely, LiCoO 2, LiNiO 2, LiNi} y Co 1-y O 2 (y = 0.01~0.99), LiMnO 2, LiCo x Mn y Ni z O 2 (x + y + z = 1) and, like LiMn ₂ O ₄ or LiFePO ₄ is used as a mixture of one kind alone or in combination.

  Among these, since the battery characteristics are superior to others, a lithium cobalt composite oxide and a heterogeneous metal element-added lithium cobalt composite oxide are often used. However, cobalt is expensive and has a small abundance as a resource. For this reason, research and development of cheaper positive electrode active material materials, such as nickel cobalt lithium manganate and the like, which can replace lithium cobalt oxide, have been vigorously conducted.

For example, in Patent Document 1 below, as a positive electrode material, LiNi _1-xy Co _x Mn _y O ₂ (where x and y are 0.5 <x + y <1.0 and 0.1 <y <0, respectively). And a lithium nickel cobalt manganese composite oxide represented by the following formula: Li _{(1 + a)} Mn _{2- ab-} MbO ₄ (wherein M is Al, Co , Ni, Mg, Fe, and at least one element selected from the group consisting of: 0 ≦ a ≦ 0.2 and 0 ≦ b ≦ 0.1. There is disclosed a technique for achieving both improvement in thermal stability and discharge capacity by mixing lithium manganese composite oxide.

In Patent Document 2 below, a specific cyclic carbonate is contained in the non-aqueous electrolyte so that a film is formed on the surface of the carbon material as the negative electrode active material to improve the charge / discharge cycle characteristics. in the nonaqueous electrolyte secondary battery selection, as a positive electrode active material, in the composition formula _{Li x Mn 2-y1 M1 y2} O 4 + z ( wherein having a spinel structure, M1 is Al, Co, Ni, Mg, from the group consisting of Fe At least one element that satisfies the following conditions: 0 ≦ x ≦ 1.5, 0 ≦ y1 ≦ 1.0, 0 ≦ y2 ≦ 0.5, and −0.2 ≦ z ≦ 0.2. And a lithium nickel compound represented by the composition formula Li _a Ni _b Co _c Mn _d O ₂ (where 0 ≦ a ≦ 1.2, b + c + d = 1 is satisfied). Combined with cobalt manganese complex oxide It is, output characteristics and charge-discharge cycle life is improved nonaqueous electrolyte secondary battery is disclosed to be obtained.

Japanese Patent Laid-Open No. 2005-267956 JP 2004-146363 A JP 2000-106174 A

  On the other hand, the development of inexpensive and high capacity non-aqueous electrolyte secondary batteries is demanded due to the demand for increased power consumption and long-time driving with the enhancement of entertainment functions such as video playback and game functions in recent mobile information terminals. Development of a technology for increasing the capacity of a nonaqueous electrolyte secondary battery in the case where nickel cobalt lithium manganate, which is cheaper than lithium cobaltate, is used as the positive electrode active material is underway.

As a method of increasing the capacity of the non-aqueous electrolyte secondary battery,
(1) Increase the capacity of the active material,
(2) Increase the charging voltage,
(3) Increase the filling amount of the active material to increase the filling density,
Such a method is conceivable.

  Problems that non-aqueous electrolyte secondary batteries having a high charge voltage have generally include a decrease in cycle characteristics and an increase in battery thickness due to gas generation. The present inventor investigated the cycle characteristics in a high temperature environment when nickel cobalt lithium manganate was used as the positive electrode active material and the charge potential of the positive electrode was higher than 4.4 V on the basis of lithium. In comparison, although the capacity decrease at the beginning of the cycle is small, it has been found that there is a problem that a rapid capacity decrease is observed after a certain number of cycles.

  Furthermore, as a result of analyzing the battery used by the inventor for investigating the cycle characteristics, nickel cobalt lithium manganate as the positive electrode active material has a smaller amount of transition metal dissolved in the electrolyte than lithium cobaltate. It was found that the amount of gas generated by the decomposition of the electrolyte and the amount of metallic lithium deposited on the negative electrode were large.

  From the results of this analytical investigation, the reason why the above-described charge / discharge cycle characteristics are observed when lithium nickel cobalt manganate is used as the positive electrode active material is estimated as follows. That is, it is considered that the decrease in the capacity of the nickel cobalt lithium manganate at the beginning of the cycle is small because the elution amount of the transition metal component is small and the capacity decrease of the positive electrode active material itself is small. On the other hand, a large amount of lithium nickel cobalt manganate gas generation indicates that a side reaction has occurred during charging, and the negative electrode side is excessively charged as compared with the positive electrode.

  This excessive charge amount does not contribute to the discharge and accumulates on the negative electrode side as an irreversible capacity. Originally, the non-aqueous electrolyte secondary battery is designed so that the negative electrode has a larger charge capacity than the positive electrode, but when the irreversible capacity gradually accumulates on the negative electrode side as described above, when a predetermined number of cycles elapses In this case, the capacity balance is lost in which the charge capacity between the positive and negative electrodes is reversed. Therefore, after a predetermined number of cycles have elapsed, metallic lithium is deposited on the negative electrode side during charging, and it is assumed that a rapid capacity reduction occurs.

  The present invention has been made to solve the above-described problems of the prior art, and uses nickel cobalt lithium manganate as the positive electrode active material, and the charge potential of the positive electrode is higher than 4.4 V on the basis of lithium. Even if it is a case, it aims at providing the nonaqueous electrolyte secondary battery excellent in the high temperature cycling characteristic.

In Patent Document 3, a positive electrode material mixture paste having a positive electrode active material that reversibly reacts with lithium such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O _{4 and the} like as a main constituent material and showing alkalinity, A non-aqueous electrolyte secondary battery using a positive electrode plate coated on a metal current collector corrosive to alkali, wherein 100 to 10000 ppm by weight of MoO ₃ is added to the positive electrode active material. An invention of a non-aqueous electrolyte secondary battery is disclosed.

The addition of MoO ₃ to the positive electrode mixture paste in Patent Document 3 is made to reduce the corrosion of the metal current collector and improve the coating property of the positive electrode mixture paste. Regarding the high-temperature cycle characteristics when a specific amount of molybdenum oxide is added to the positive electrode active material mixture when nickel-cobalt lithium manganate is used and the charge potential of the positive electrode is higher than 4.40 V with respect to lithium Nothing has been considered.

In order to achieve the above object, the nonaqueous electrolyte secondary battery of the present invention comprises:
A positive electrode plate having a positive electrode active material mixture layer containing a positive electrode active material capable of occluding and releasing lithium ions, and a negative electrode active material mixture layer containing a negative electrode active material capable of occluding and releasing lithium ions. In a non-aqueous electrolyte secondary battery comprising a negative electrode plate and a non-aqueous electrolyte,
Li _a Ni _x Co _y Mn _1-xy O ₂ (0.9 ≦ a ≦ 1.1, 0 <x <1, 0 <y <1, 2x ≧ 1-y) as the positive electrode active material Containing at least 1% by mass of nickel cobalt lithium manganate represented,
The positive electrode active material mixture layer contains molybdenum oxide (MoO _z ; 2 ≦ z ≦ 3) in an amount of 0.01 to 3.0% by mass with respect to lithium nickel cobalt manganate. .

  According to the nonaqueous electrolyte secondary battery of the present invention, even when lithium nickel cobalt manganate is used as the positive electrode active material and the charging potential of the positive electrode is higher than 4.4 V on the basis of lithium, As a result, a non-aqueous electrolyte secondary battery with excellent high-temperature cycle characteristics is obtained in which the capacity retention rate after charge / discharge cycles in a high-temperature environment is improved and the increase in battery thickness is also suppressed. It is done.

The above effect of the present invention is presumed to be caused by the following mechanism of action.
That is, molybdenum dioxide, molybdenum oxide, and their non-stoichiometric composition have a reaction potential in the range of 1.0 to 2.5 V with respect to the potential of lithium, so that oxidation mixed in the positive electrode active material mixture Molybdenum does not contribute to the charge / discharge reaction itself, but is characterized by being gradually chemically dissolved.

  Molybdenum ions dissolved in the electrolytic solution diffuse to the negative electrode side and are eventually reduced on the negative electrode. This reduction reaction has a function of correcting a capacity balance disruption in which the capacity ratio of the positive electrode and the negative electrode (= negative electrode charge capacity / positive electrode charge capacity) is less than 1 due to gas generation on the positive electrode. In other words, it is considered that the cycle characteristics are improved because the capacity balance collapse is corrected by the action that the excessive charge amount accumulated on the negative electrode side is consumed by the dissolution and precipitation of molybdenum oxide.

  In addition, considering the deposition pattern of metal cations, concentrated precipitation occurs when the growth reaction is faster than the nucleation reaction, and precipitation occurs in a relatively dispersed state when the nucleation reaction is faster than the growth reaction. . This difference in the form of precipitation is peculiar to the element (ion species). For example, copper ions, nickel ions, etc. are relatively concentrated.

  When such concentrated precipitation occurs, the active site of the negative electrode is blocked, the lithium intercalation reaction is inhibited, and when the precipitation proceeds further, the separator penetrates and the positive and negative electrodes are locally short-circuited. The phenomenon to be seen is seen. The battery in such a state cannot be charged / discharged normally.

  On the other hand, since molybdenum precipitates in a dispersed state, it is considered that the active site of the negative electrode is not easily blocked, and inhibition of the intercalation reaction is suppressed. That is, the oxide to be mixed in the positive electrode mixture is not limited, and it is necessary to take into consideration the form of precipitation. In this respect, molybdenum oxide is considered to be superior to other oxides or metals.

  For the same reason as described above, the molybdenum oxide mixed in the positive electrode material is preferably in a uniformly dispersed state, and the particle diameter is preferably small. Specifically, in the particle size distribution measured by a laser diffraction method, it is preferable that D50 is 5 to 10 μm and D90 is 30 μm or less.

  In addition, lithium nickel cobalt manganate has a lower true density and lower fillability than lithium cobalt oxide. Therefore, when trying to achieve both high energy density and cost reduction of the cathode active material, a mixture of at least one of lithium cobaltate, nickel nickelate and nickel cobaltate having a high filling property is used as the cathode active material. Is effective.

  Further, in the present invention, as a negative electrode active material, carbon materials such as graphite and coke capable of reversibly occluding and releasing lithium ions, metals that can be alloyed with lithium such as tin oxide, metallic lithium, and silicon, and Although those alloys can be used, it is preferable to use graphite among them. Furthermore, what consists of copper or a copper alloy can be used as a core of a negative electrode.

  In the present invention, the positive electrode mixture may contain a conductive agent or a binder that has been conventionally used. Moreover, what consists of aluminum or an aluminum alloy can be used as a core of a positive electrode.

  In the present invention, as the nonaqueous solvent for the nonaqueous electrolyte, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC), fluorinated cyclic carbonates, and γ-butyrolactone are used. (BL), cyclic carboxylic acid esters such as γ-valerolactone (VL), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), dibutyl carbonate (DBC), etc. Chain carbonic acid esters, fluorinated chain carbonic acid esters, methyl pivalate, ethyl pivalate, methyl carboxylic acid esters such as methyl isobutyrate, methyl propionate, N, N′-dimethylformamide, N— Methyloxazolid Amide compounds such emissions, sulfur compounds such as sulfolane, and the like may be employed a room temperature molten salt, such as tetrafluoroborate, 1-ethyl-3-methyl imidazolium. It is preferable to use a mixture of two or more of these. In particular, in order to increase ionic conductivity, it is more preferable to use a mixture of a cyclic carbonate having a high dielectric constant and a chain carbonate having a low viscosity.

  In the present invention, as a compound for stabilizing the electrode in the non-aqueous electrolyte, vinylene carbonate (VC), vinyl ethyl carbonate (VEC), succinic anhydride (SUCAH), maleic anhydride (MAAH), glycol An acid anhydride, ethylene sulfite (ES), divinyl sulfone (VS), vinyl acetate (VA), vinyl pivalate (VP), catechol carbonate, biphenyl (BP) and the like may be added. Two or more of these compounds can be appropriately mixed and used.

In the present invention, a lithium salt generally used as an electrolyte salt in a nonaqueous electrolyte secondary battery can be used as an electrolyte salt dissolved in a nonaqueous solvent. Such lithium salts include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , and mixtures thereof Illustrated. Among these, LiPF ₆ (lithium hexafluorophosphate) is particularly preferable. The amount of electrolyte salt dissolved in the non-aqueous solvent is preferably 0.8 to 1.5 mol / L.

  Furthermore, in the non-aqueous electrolyte secondary battery of the present invention, the non-aqueous electrolyte may be not only liquid but also gelled.

6 is a graph showing the relationship between the number of cycles and the capacity retention rate with respect to Example 1 and Comparative Example 1. 10 is a graph showing the relationship between the number of cycles and the capacity retention rate in Comparative Examples 5 and 6.

  Hereinafter, the form for implementing this invention is demonstrated in detail using an Example and a comparative example. However, the following examples illustrate non-aqueous electrolyte secondary batteries for embodying the technical idea of the present invention, and are not intended to specify the present invention to these examples. The present invention can be equally applied to various modifications without departing from the technical idea shown in the claims.

[Example 1]
[Positive electrode active material]
The nickel cobalt lithium manganate as the positive electrode active material was obtained as follows. As a starting material, lithium hydroxide (LiOH.H ₂ O) was used as a lithium source. As the transition metal source, nickel, cobalt and manganese coprecipitated hydroxides (Ni _0.33 Co _0.34 Mn _0.33 (OH) ₂ ) were used. These were weighed and mixed so that the molar ratio of lithium to transition metal (nickel, cobalt and manganese) was 1: 1. The obtained mixture was calcined at 400 ° C. for 12 hours in an oxygen atmosphere and crushed in a mortar, and further calcined at 900 ° C. for 24 hours in an oxygen atmosphere to obtain lithium nickel cobalt manganate. This was pulverized with a mortar until the average particle size became 15 μm to obtain a positive electrode active material used in this example. The chemical composition of nickel cobalt lithium manganate was measured by ICP (Inductively Coupled Plasma).

[Preparation of positive electrode active material mixture slurry]
To the nickel cobalt lithium manganate as the positive electrode active material obtained as described above, 0.1% by mass of molybdenum trioxide (MoO ₃ ) was added and mixed, and the positive electrode active material and molybdenum trioxide were mixed. A mixture was obtained.
To 96 parts by mass of this mixture, 2 parts by mass of carbon powder as a conductive agent and 2 parts by mass of polyvinylidene fluoride powder as a binder are mixed, and this is mixed with an N-methylpyrrolidone (NMP) solution. Thus, a positive electrode active material mixture slurry was prepared.

[Preparation of positive electrode plate]
The positive electrode active material mixture slurry obtained as described above was applied to both surfaces of an aluminum positive electrode core having a thickness of 15 μm by a doctor blade method so that the coating mass was 21.2 mg / cm ^{2 on} one side and 42.4 mg / cm on both sides. cm ^2, coated portion of one surface of 277 mm, uncoated portion 57 mm, the application portion of the other surface 208 mm, uncoated portions so as to give a 126 mm. Then, the positive electrode active material mixture layer was formed on both surfaces of the positive electrode core body by passing through a dryer and drying. Subsequently, the positive electrode plate used for a present Example was obtained by compressing so that the thickness of a double-sided application part might be 132 micrometers using a compression roller.

[Production of negative electrode plate]
An appropriate amount of 97.5 parts by mass of graphite as a negative electrode active material, 1.0 part by mass of carboxymethyl cellulose (CMC) as a thickener, and 1.5 parts by mass of styrene butadiene rubber (SBR) as a binder. Was mixed with water to obtain a negative electrode active material mixture slurry. By a doctor blade method on both surfaces of a copper negative electrode substrate having a thickness of 10μm to the negative electrode active material mixture slurry, 11.3 mg / cm ² coating amount on one side, 22.6 mg / cm ² on both sides, the coating of one surface The coating was performed so that the portion was 284 mm, the uncoated portion was 33 mm, the coated portion on the other surface was 226 mm, and the uncoated portion was 91 mm. Then, the negative electrode active material mixture layer was formed on both surfaces of the negative electrode core by passing through a dryer and drying. Subsequently, the negative electrode plate used for a present Example was obtained by compressing so that the thickness of a double-sided application part might be set to 155 micrometers using a compression roller.

  Note that the potential of graphite during charging is about 0.1 V on the basis of Li. Moreover, the active material filling amount of the positive electrode and the negative electrode was adjusted such that the charge capacity ratio of the positive electrode to the negative electrode (negative electrode charge capacity / positive electrode charge capacity) was 1.1 at the potential of the positive electrode active material which is a design standard.

[Preparation of electrolyte]
After dissolving lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1 mol / L in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 3: 7 The electrolyte solution used for a present Example was prepared by adding 1 mass% of vinylene carbonate (VC).

[Production of flat wound electrode body]
After the positive electrode plate and the negative electrode plate manufactured as described above were welded with an aluminum lead wire on the positive electrode plate and a nickel lead wire on the negative electrode plate, from the polyethylene microporous film The spiral electrode body used in the present example was manufactured by winding it in a flat shape through the separator.

[Preparation of non-aqueous electrolyte battery]
The flat wound electrode body produced as described above was sealed in a laminate container, and the electrolytic solution obtained as described above was injected in a glove box filled with Ar. Then, the non-aqueous electrolyte secondary battery (design capacity: 800 mAh) concerning a present Example was produced by plugging a liquid injection port.

[Examples 2 and 3]
In Examples 2 and 3, non-aqueous electrolyte secondary batteries were produced in the same manner as in Example 1 except that the composition ratio of nickel, cobalt, and manganese in lithium nickel cobalt lithium manganate was changed.

[Examples 4 to 6]
In Examples 4 to 6, a mixture obtained by mixing lithium nickel cobalt manganate and lithium cobalt oxide used in Examples 1 and 2 at a predetermined mixing ratio was used as the positive electrode active material. Further, in Example 6, A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the amount of MoO ₃ mixed was changed to 0.01 mass% with respect to the positive electrode active material.

Lithium cobaltate as a positive electrode active material was obtained as follows. As a starting material, lithium carbonate (Li ₂ CO ₃ ) was used as a lithium source. As the cobalt source, tricobalt tetroxide (Co ₃ O ₄ ) obtained by calcining cobalt carbonate at 550 ° C. and thermal decomposition reaction was used. These were weighed so that the molar ratio of lithium to cobalt was 1: 1 and mixed in a mortar. The obtained mixture was baked at 850 ° C. for 20 hours in an air atmosphere to obtain lithium cobalt oxide. This was ground to an average particle size of 15 μm with a mortar to obtain a positive electrode active material. The chemical composition of lithium cobaltate was measured by ICP (Inductively Coupled Plasma).

[Examples 7 and 8 and Comparative Example 4]
In Examples 7 and 8 and Comparative Example 4, non-aqueous electrolyte secondary batteries were produced in the same manner as in Example 1 except that the content of MoO ₃ in the positive electrode active material mixture was changed.

[Example 9]
In Example 9, a molybdenum oxide to be added to the positive electrode active material material mixture, except for changing the MoO ₂ was used to fabricate a non-aqueous electrolyte secondary battery in the same manner as in Example 1.

[Comparative Examples 1-3]
In Comparative Examples 1 to 3, non-aqueous electrolyte secondary batteries were produced in the same manner as in Examples 1, 2 and 4 except that molybdenum oxide was not added.

[Comparative Examples 5 and 6]
In Comparative Examples 5 and 6, a non-aqueous electrolyte secondary battery was manufactured using only lithium cobaltate instead of nickel cobalt lithium manganate as the positive electrode active material. The difference between the two is the presence or absence of addition of molybdenum oxide.

[High voltage high temperature cycle characteristics test]
About the nonaqueous electrolyte secondary battery concerning each Example and comparative example produced as mentioned above, the high voltage high temperature cycling characteristic test was done on condition of the following.
-Charging: Constant current charging is performed at a current of 1.0 It (800 mA) until the battery voltage reaches 4.4 V (the positive electrode potential is 4.5 V based on lithium), and then the current value is 1 at a constant voltage of 4.4 V. The battery was charged until / 20 It (40 mA).
Discharge: Constant current discharge was performed until the battery voltage became 3.0 V at a current of 1.0 It (the positive electrode potential was 3.1 V based on lithium).
-Pause: The pause interval from the completion of charging to the start of discharging and from the end of discharging to the start of charging was 10 minutes each.
-Environmental temperature: It implemented in the 45 degreeC thermostat.
Charging-resting-discharging-resting under the above conditions is one cycle of charging / discharging, the charging / discharging cycle is repeated 200 cycles, and the value obtained from the following calculation formula from the first discharging capacity and the 200th discharging capacity: Was obtained as the capacity retention rate (%) after 200 cycles.
Capacity maintenance rate after 200 cycles (%)
= (200th cycle discharge capacity / 1st cycle discharge capacity) × 100

In addition, before and after the cycle characteristic test, the battery thickness was measured for each of the examples and comparative examples, and the amount of increase in battery thickness by continuous charge / discharge 200 cycles (battery thickness after cycle test−before cycle test). Battery thickness).
These results are summarized in Table 1.

  For Example 1 and Comparative Examples 1, 5 and 6, the discharge capacity was measured for each charge / discharge cycle, the capacity retention rate after each cycle was calculated, and the transition of the capacity decrease accompanying repeated charge / discharge was confirmed. did. A comparison between Example 1 and Comparative Example 1 is shown in FIG. 1, and a comparison between Comparative Example 5 and Comparative Example 6 is shown in FIG.

From the results shown in Table 1 and FIGS.
That is, the nonaqueous electrolyte secondary batteries of Examples 1-3, 7 and 8 that use nickel cobalt lithium manganate as the positive electrode active material and contain molybdenum oxide in the positive electrode active material mixture include molybdenum oxide. Compared with Comparative Examples 1 and 2 that do not, the capacity retention rate after 200 cycles is high, and the increase in battery thickness is small.

  Referring to FIG. 1, in Comparative Example 1 in which the positive electrode active material mixture does not contain molybdenum oxide, the capacity rapidly deteriorates in 50 to 100 cycles. This inflection point indicates the timing when the capacity ratio between the positive electrode and the negative electrode (= negative electrode charging capacity / positive electrode charging capacity) is divided by 1, and it is assumed that Li metal begins to precipitate on the negative electrode at this point. The

  On the other hand, in Example 1, a rapid capacity drop does not occur and good cycle characteristics are shown. From this, by adding molybdenum oxide to the positive electrode active material mixture, the above-mentioned effect of the present invention is produced by suppressing the collapse of the capacity balance in which the capacity ratio between the positive electrode and the negative electrode is less than 1. It is thought that.

  In Comparative Examples 5 and 6 using only lithium cobaltate as the positive electrode active material, there is no difference in capacity retention after 200 cycles depending on whether or not molybdenum is added. Referring to FIG. 2, it can be confirmed that in Comparative Example 5 in which the positive electrode active material mixture does not contain molybdenum oxide, there is no sudden capacity decrease as seen in Comparative Example 1. There is no difference in cycle characteristics between 5 and 6.

  This is because lithium cobaltate has fewer side reactions during charging than nickel cobalt lithium manganate, and therefore, cobalt dissolves and is reduced and deposited on the negative electrode. It is presumed that no collapse has occurred. Therefore, when only lithium cobaltate is used as the positive electrode active material, the above effect due to the addition of molybdenum to the positive electrode active material mixture does not occur.

  Further, in Examples 4 to 6 in which nickel cobalt lithium manganate and lithium cobaltate were mixed and used as the positive electrode active material, good cycle characteristics were shown as compared with Comparative Example 3, and nickel cobalt lithium manganate was used. It can be seen that the above-described effects can be obtained even when a mixture of lithium cobalt oxide is used as the positive electrode active material. Therefore, as long as it contains at least nickel cobalt lithium manganate as the positive electrode active material, even when using a mixture with other lithium transition metal composite oxides such as lithium nickelate and lithium nickel cobaltate, It is suggested that the above effect is achieved by adding molybdenum to the positive electrode active material mixture.

  In addition, since nickel cobalt lithium manganate has a lower true density than lithium cobaltate and inferior fillability, cobalt oxide with high fillability can be used to achieve both high energy density and cost reduction of the positive electrode active material. It is useful to mix lithium, lithium nickelate, nickel cobaltate, or the like and nickel cobalt lithium manganate as a positive electrode active material. In such a case, the present invention can be applied.

Further, from the results of Example 9, is added to molybdenum oxide is seen that the effects of the present invention there is provided a MoO ₂ is effectively achieved.

  About the addition amount of molybdenum oxide in a positive electrode active material mixture, it turns out from the result of Example 6 that the effect of this invention will be show | played if it is 0.01 mass% or more with respect to a positive electrode active material. On the other hand, in Comparative Example 4, although the effect of suppressing the battery swelling after 200 cycles was recognized as compared with Comparative Examples 1 to 3, the capacity retention rate after 200 cycles was extremely reduced, and the positive electrode active material It can be seen that addition of an excessive amount of molybdenum oxide such as 5.0% by mass or more is not preferable.

  This is because the amount of molybdenum oxide added is excessive, and molybdenum oxide (molybdenum ions) dissolved from the positive electrode precipitates in a large amount on the negative electrode, thereby blocking the active site of the negative electrode material, resulting in a lithium intercalation reaction. It is presumed that this has been hindered.

  Further, from the results of Examples 7 and 8, it can be seen that when the addition amount of molybdenum oxide is 2.0% by mass or less with respect to the positive electrode active material, the above-described extreme decrease in the capacity retention rate does not occur. .

  Therefore, when interpolating from the results of Example 8 and Comparative Example 4, the amount of molybdenum oxide added to the positive electrode active material mixture is limited to about 3.0% by mass with respect to the positive electrode active material. It is preferable to keep it.

Claims (4)

A positive electrode plate having a positive electrode active material mixture layer containing a positive electrode active material capable of occluding and releasing lithium ions, and a negative electrode active material mixture layer containing a negative electrode active material capable of occluding and releasing lithium ions. In a non-aqueous electrolyte secondary battery comprising a negative electrode plate and a non-aqueous electrolyte,
The positive electrode active material is represented by LiNi _x Co _y Mn _1-xy O ₂ (0.9 ≦ a ≦ 1.1, 0 <x <1, 0 <y <1, 2x ≧ 1-y). Containing at least 1% by mass of nickel cobalt lithium manganate,
The positive electrode active material mixture layer contains molybdenum oxide (MoO _z ; 2 ≦ z ≦ 3) in an amount of 0.01 to 3.0% by mass with respect to lithium nickel cobalt manganate. Non-aqueous electrolyte secondary battery.   2. The non-aqueous solution according to claim 1, wherein the positive electrode active material is a mixture of lithium nickel cobalt manganate and at least one selected from lithium cobaltate, lithium nickelate, and lithium nickel cobaltate. Electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is graphite.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a charge potential of the positive electrode plate is 4.40 V or more based on lithium.

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